Safety first when canning garden produce

A variety of food preservation questions are asked every year as home gardeners go to work harvesting garden produce and want to “put it up” or “can” it for food storage. So, in an effort to respond to some of the most frequently asked questions, the Center for Home Food Preservation (NCHFP) offers the following tips and advice.

Is it necessary to sterilize jars before canning?

Jars do not need to be sterilized before canning if they will be filled with food and processed in a boiling water bath canner for 10 minutes or more or if they will be processed in a pressure canner. Jars that will be processed in a boiling water bath canner for less than 10 minutes, once filled, need to be sterilized first by boiling them in hot water for 10 minutes before they're filled. (Note: There are no boiling water bath recipes at our altitudes with processing times of 10 minutes or less.)

Do I need to leave a certain amount of headspace in the jar?

Yes, leaving the specified amount of headspace in a jar is important to assure a vacuum seal. If too little headspace is allowed the food may expand and bubble out when air is being forced out from under the lid during processing. The bubbling food may leave a deposit on the rim of the jar or the seal of the lid and prevent the jar from sealing properly. If too much headspace is allowed, the food at the top is likely to discolor. Also, the jar may not seal properly because there will not be enough processing time to drive all the air out of the jar.

Can two layers of jars be processed in a canner at one time?

Yes, two layers can be processed at one time, in either the boiling water bath or pressure canner. Place a small wire rack between the layers so water or steam will circulate around each jar. Make certain that the water covers the tops of all jars by one inch in a boiling water bath canner. The pressure canner should have two to three inches of water in the bottom.

Is it all right to reuse jar fittings (lids and bands)?

Lids should not be used a second time since the sealing compound becomes indented by the first use, preventing another airtight seal. Screw bands may be reused unless they are badly rusted or the top edge is pried up which would prevent a proper seal.

What causes jars to break in a canner?

Breakage can occur for several reasons: 1. Using commercial food jars rather than jars manufactured for home canning, 2. Using jars that have hairline cracks, 3. Putting jars directly on bottom of canner instead of on a rack, 4. Putting hot food in cold jars, or 5. Putting jars of raw or unheated food directly into boiling water in the canner, rather than into hot water (sudden change in temperature-too wide a margin between temperature of filled jars and water in canner before processing).

What can I process in half-gallon canning jars?

At least one canning jar manufacturer is selling half-gallon canning jars. That manufacturer has a printed note on the top that says half-gallon jars are only used for some highly acidic foods in a boiling water canner, with instructions to call a toll-free number for the instructions. The only recommended choices are grape juice and apple juice.

Why is canning summer squash or zucchini not recommended?

Recommendations for canning summer squashes, including zucchini, have been withdrawn due to uncertainty about the determination of processing times. Squashes are low-acid vegetables and require pressure canning for a known period of time that will destroy the bacteria that cause botulism. Documentation for the previous processing times cannot be found, and reports that are available do not support the old process. Slices or cubes of cooked summer squash will get quite soft and pack tightly into the jars. The amount of squash filled into a jar will affect the heating pattern in that jar. It is best to freeze summer squashes or pickle them for canning, but they may also be dried.

For additional help, contact your local USU Extension Office or see nchfp.uga.edu.

Kathleen Riggs is the Utah State University Extension family and consumer sciences professor for Iron County. Email her kathleen.riggs@usu.edu or call 435-586-8132.